World football's governing body, already reeling from a string of corruption claims, has been thrown into fresh turmoil by serious bribery allegations concerning two of the most senior figures on Fifa's executive committee.

Fifa announced that the longstanding executive committee member Chuck Blazer had accused Mohamed bin Hammam, the challenger to Sepp Blatter in the presidential election next week, of offering bribes to members of the Caribbean Football Union (CFU) at a meeting organised by the Fifa vice‑president, Jack Warner, two weeks ago.

Bin Hammam and Warner immediately denied the allegations – understood to include claims that large amounts of cash were offered – from witnesses who have signed affadavits, and accused Blatter of using them as a "tactic" to win the election.

A file of evidence compiled by a Chicago attorney who also sits on Fifa's legal committee contains claims that members of the CFU were offered thousands of dollars in cash for "development projects" by Warner on behalf of Bin Hammam.

Fifa said an investigation into the allegations would be undertaken by its ethics committee immediately. It is due to consider the charges at a hastily convened meeting on Sunday.

The new claims, which mean that nine of Fifa's 24 executive committee members have been accused of corruption in recent months, threaten to throw next week's Fifa congress into chaos and raise question marks over whether the election will even go ahead. Bin Hammam immediately accused Blatter of using the charges to undermine his chances. Although Blatter has won the support of five of the six confederations that make up Fifa, previous elections have shown the potential for dramatic last minute vote switching by the 208 members with a vote, often amid allegations of impropriety.

That the allegations were made by Blazer, himself a key member of the Concacaf confederation that has afforded Warner a king-making role in successive Fifa presidential elections and World Cup bids – despite persistent allegations of corruption – adds another layer of intrigue.

There was a widespread suspicion among members of the USA's failed 2022 bid that Warner had in fact voted against them in December. As in England, in the wake of their bid humiliation there was widespread outrage from the US media amid calls for reform and Blazer may have come under pressure to act. The four accused – Bin Hammam and Warner plus the CFU officials Debbie Minguell and Jason Sylvester – have been invited to respond to the allegations by Friday and to attend a hearing in Zurich on Sunday. Bin Hammam said he is confident he would be absolved of all charges. "This has been a difficult and painful day for me today. But, if there is even the slightest justice in the world, these allegations will vanish in the wind," he said. "This move is little more than a tactic being used by those who have no confidence in their own ability to emerge successfully from the Fifa presidential election. I completely deny any allegations of wrongdoing either intentionally or unknowingly while I was in the Caribbean.."

Warner responded: "I am not aware of any wrongdoing on my part and I shall listen to allegations made and respond accordingly. It is interesting to note the timing of these allegations and [that] the hearing [is] scheduled days before the Fifa presidential elections."

The meeting of the CFU took place between 10‑11 May, after Bin Hammam was unable to travel to the earlier Concacaf congress in Miami, at which Blatter was present, due to visa issues.

Blatter had left the congress convinced he had done enough to secure all 35 votes on offer if Warner managed to ensure that the whole confederation voted en bloc. But the US had already made clear that it would consider its decision independently. "We'll make a decision that's in the best interests of US Soccer and what we think is good for the game internationally," said president Sunil Gulati.

After the CFU meeting Warner, who was one of four Fifa executives accused by the former FA chairman Lord Triesman of seeking inducements during the 2018 bid campaign andhas been embroiled in repeated controversies over tickets, urged the 30 associations present to ignore any future allegations. "You will hear the president of Asia came here for your vote and he gave you, a Benz for you, a Benz for you and a Benz for you," he said. "When you go back home, you hold your head high and you will tell your members that you were not part of this international nonsense."

Blatter will see the bribery claims as beneficial to his chances of winning the election but the farcical situation will further increase pressure on Fifa from governments and the public for wholesale reform.

"It is difficult to comment from England's viewpoint in advance of James Dingemans report [into earlier corruption made by former chairman Lord Triesman] commisioned by the FA," said the sports minister Hugh Robertson last night. "But it does emphasies once again the need for much greater transparency and governance reform at Fifa."

Last October two executive committee members – Amos Adamu and Reynald Temarii – were suspended following a Sunday Times investigation and four more – Warner, Nicolás Leoz, Ricardo Teixeira and Worawi Makudi – were this month accused by the former FA chairman Lord Triesman of seeking inducements during the 2018 bidding process.

John Collins, a Chicago attorney and a member of Fifa's legal committee, prepared the dossier after being approached by concerned CFU officials. He last night told the Guardian: "I conducted the investigation and prepared a report and sent it to Fifa at Chuck Blazer's direction. It is a thorough report."

Alongside signed affadavits from CFU officials present, it is understood that the report contains photographic evidence.